In aqueous dispersion materials containing functional substances, it is conventionally well known to contain, as functional materials, agricultural chemicals such as herbicides and insecticides; pharmaceuticals such as carcinostatics, antialergic agents and antiphlogistics; and materials for coloring, such as inks and toners having coloring materials.
In recent years, digital printing technique is making very dramatic progress. This digital printing technique is, as its typical example, what is called electrophotographic technique or ink jet technique, and is more and more making its presence felt as an image forming technique in offices, homes and so forth. Meanwhile, a trend toward the use of such an image forming technique in the fabrication of devices such as semiconductor devices and display devices is also becoming active, and this technique is being widely developed not only in image formation but also in industrial uses.
In particular, the ink jet technique has great characteristic features that it can enjoy compactness and low power consumption as a direct recording method. Also, image quality is being rapidly made higher as nozzles are made finer. An example of the ink jet technique is a method in which an ink fed from an ink tank is heated with heaters in nozzles to cause evaporation to bubbling, whereupon the ink is ejected to form images on a recording medium. Another example is a method in which the ink is ejected from nozzles by vibrating piezoelectric elements.
As inks used in such methods, aqueous dye solutions are usually used, and hence colors may blur when they are superimposed, or a phenomenon called feathering may come in the direction of fibers of paper at recorded areas on a recording medium. Also, since dyes are chiefly used as coloring materials, it is earnestly demanded to improve weatherability. For the purpose of making improvements on these, an example is found in which the reaction of a dye ink with a pigment ink is utilized (U.S. Pat. No. 5,320,668). An example is also found in which a reactive self-dispersible pigment is used (U.S. Pat. No. 6,281,267).